Small plate-shaped crystals of sulfite oxidase, a molybdenum containing enzyme, have been obtained under two different pH conditions. Sulfite oxidase is a molybdopterin enzyme, of which there are three families: the xanthine oxidase family; the DMSO reductase family; and the sulfite oxidase family. Crystal structures of enzymes in the first two families have recently been solved, however, there is no structure available from the sulfite oxidase family. Preliminary experiments have shown that synchrotron radiation sources and the rotation camera are required to obtain x-ray diffraction data from these small plate-shaped crystals of sulfite oxidase.